The present invention relates to an adhesive film based on polyvinyl chloride (PVC) in particular for use in a method of making a decoration of graphi. In particular aspect, the invention relates to a method of applying a graphic to a substrate such as a building or a vehicle using a PVC based adhesive film.
PVC based adhesive films have been widely used in producing graphics or decorations on substrates. For example adhesive films are used to provide advertisement, logos or company names and information on vehicles such as vans, busses, trains, trams etc. They may also be used on buildings. Typically, the adhesive film will have to remain in place for an extended period of time up to several years. Accordingly, the graphics produced with the film are exposed to a large variety of weather conditions. Particularly in so called horizontal applications, where the film is applied over a generally horizontal surface such as on the hood of a car, the weathering conditions may be particularly severe. Accordingly, the adhesive film needs to have excellent weathering stability and excellent adhesion characteristics to the surface.
Yet, after use, it is generally desirable that the graphic film can be removed without damaging the surface of the substrate which frequently may be a painted surface. In certain applications, these graphics may be of a significant size. Adhesion of a large image graphic film to substrates encounters the problem of entrapped air between the film and the substrate. Anyone who has ever attempted to hang wallpaper can appreciate the frustration that can arise when entrapped air beneath an adhesive-backed film can not be removed easily. The removal of air bubbles is labor intensive. The art has provided multiple solutions to this problem by providing air-bleed channels in the adhesive. For example, EP 951518 discloses the use of channels in the adhesive to allow air bleed during application of the graphic film. In certain instances it has been found that the presence of air bleed channels may become visible on the graphic and disturb the appeal of the graphic. Such may occur shortly after application of the film or develop over an extended period of time.
Still further, the surface of the substrate may be uneven requiring good conformability of the film. For example, when the film is used in personalization of vehicles or in decorating vehicles, the film may need to be applied over recesses such as where the license plate is located, over curved surfaces such as over bumpers and/or other complex contours of the substrate. As a result of stress relaxation of the film following the application on the substrate, the adhesive film may lift and pop-up in areas where the surface of the substrate is uneven or has a complex shape. This undesired behavior may become apparent shortly after application or after some time.
Also, when applying the film over an uneven substrate with a complex shape, so called “whitening at stress” may occur leading to a more or less pronounced color change and/or change in gloss of the graphic film.
In certain methods for producing graphics, the PVC adhesive is cut in a plotter, so-called electro cutting whereby the film up to the liner protecting the adhesive is cut with a desired image, for example lettering. Following the electro-cutting, the adhesive film is weeded, whereby the undesired parts are removed from the liner, thereby leaving thereon the desired image, for example lettering. The parts removed present the negative of the image remaining on the liner. With the aid of an application tape, the image is then applied on the substrate on which the graphic is desired. To produce appealing graphics, a variety of graphic films is desired showing a wide range of colors with good vibrancy. Also, special effects films are desired producing a metallic or pearlescent look.